Various photosensitive polymers, as shown by Merrill U.S. Pat. No. 2,948,610, directed to azide polymers, Minsk U.S. Pat. No. 2,725,372, directed to unsaturated esters of polyvinyl alcohol, Eastman Kodak photoresist KPR and KMER have been used in combination with various photosensitizers to effect the cross-linking of the polymer when exposed to UV radiation.
Ito et al. U.S. Pat. No. 4,491,628 shows the use of a polymer, such as polystyrene having recurring pendant groups such as t-butyl ester or t-butyl carbonates in combination with a photoinitiator. Exposure to UV radiation generates acid which converts the styryl t-butyl ester or styryl t-butyl carbonate to the corresponding base soluble phenol. A sensitizer altering the wave-length of the sensitizer also can be added to the photoresist. Although the positive or negative photoresist compositions of Ito et al. provide particular advantages over the photoresists of the prior art, it has been found that exposure of poly-t-butoxycarbonyloxy styrene, or the corresponding poly-t-butoxycarbonyloxy-.alpha.-methylstyrene to UV radiation results in the production of both carbon dioxide and isobutylene, an excessive amount of gaseous by-products. It would be desirable to have positive or negative photoresist compositions, resulting from the use of polymeric materials which are either convertible to aqueous base soluble products, or products soluble in a mixture of n-hexane and methylene chloride, which do not generate excessive amounts of gaseous by-products.
The present invention is based on my discovery that t-substituted organomethyl vinylaryl ethers such as t-butylvinylaryl ethers having the formula ##STR1## where R is a monovalent radical selected from the class consisting of C.sub.(1-8) alkyl radicals and C.sub.(6-14) aryl radicals, R.sup.1 and R.sup.2 are the same or different C.sub.(1-8) monovalent alkyl radicals, R.sup.3 is a monovalent radical selected from hydrogen and C.sub.(1-3) alkyl, and R.sup.4 is a monovalent radical selected from hydrogen, C.sub.(1-3) alkyl and mixtures thereof, R.sup.5 is selected from the same or different C.sub.(1-8) alkyl radicals, Cl, Br, NO.sub.2, CN, C.sub.(1-8) alkoxy and C.sub.(1-8) alkyl ester and a is equal to 0 to 2 inclusive, can be polymerized and the resulting polymer can be utilized as a photoresist when combined with an effective amount of an aryl onium salt as defined hereinafter. The resulting photoresist can be converted to a positive photoresist having a plurality of chemically combined units of the formula ##STR2## where R.sup.3, R.sup.4, R.sup.5 and a are as previously defined. Advantageously, the generation of the base soluble polymer consisting essentially of chemically combined units of formula (2) can result in the production of an unsaturated olefin, such as isobutylene without the generation of additional amounts of gaseous by-products, such as carbon dioxide formed in the photoresist method of Ito et al.